This invention relates generally to low-utilization communication systems; for example, according to one embodiment, an emergency telephone in an elevator is connected to a remote station with a minimization of noise and with a reduction in the number of dedicated telephone lines needed for multiple telephones.
One of the problems associated with elevator telephones is that the telephone cable for the elevator telephone is included in the "trailing cable," which follows the elevator. That trailing cable telephone line acts as an antenna, picking up noise from a variety of sources, including switch gear for the elevator, motors for the elevator, elevator lighting, etc.
One prior art attempt at a solution to this noise problem comprises dedicating individual telephone lines to each elevator telephone, such that each elevator telephone is connected to an exterior telephone company telephone line. Such a solution is very expensive and economically inefficient because of low utilization and because of telephone company line charges. Therefore, there is a need to solve the noise problem without the use of dedicated phone lines.
To address this need, some systems use one individual telephone line which is connected in parallel to each of the elevators in a building. With this parallel connection, it has been found that the induced noise on each elevator cable is also coupled to all other elevator phone cables as well, resulting in a summation of the noise on any individual line being equal to the total amount on all telephone line cables.
There have also been attempts to connect the telephones of each elevator to an existing telephone line that is normally used for communication by tenants in the building where the elevators are located. The idea of this approach is that the normal business line of a tenant can handle the slight increase in usage caused by elevator calls. However, such a system results in the business telephone line being plagued by hum, pops, line "sing." etc., while elevators are running, due to the induced cable noise from the elevator control switching, lighting, motor starting and stopping, etc.
Therefore, there is also a need to provide an elevator telephone system that applies multiple elevator telephones to a single telephone line, and which reduces the noise generated on the elevator phones and the outside telephone line.